Processes for producing (meth)acrylonitrile by an ammoxidation reaction of propylene or isobutylene as well as processes for producing (meth)acrylic acid by an oxidation reaction of propylene or isobutylene are known in the prior art. More recently, processes for producing (meth)acrylonitrile by a vapor-phase ammoxidation reaction of propane or isobutane and processes for producing (meth)acrylic acid by a vapor-phase catalytic ammoxidation reaction of propane or isobutane are attracting attention as alternatives to such processes using propylene or isobutylene.
Patent document 1 describes a catalyst used in a vapor-phase catalytic oxidation reaction or vapor-phase catalytic ammoxidation reaction of propane or isobutane having a specific reduction ratio and specific surface area. This catalyst having the specific reduction ratio and specific surface area is described as exhibiting suitable activity, having favorable reaction performance (selectivity and yield of target product) and demonstrating little decrease in yield over time.
On the other hand, a fluidized bed reaction is preferable for the reaction form used for vapor-phase catalytic oxidation or vapor-phase catalytic ammoxidation for reasons such as facilitating dissipation of reaction heat enabling the temperature of the catalyst layer to be maintained nearly uniformly, and facilitating removal or addition of catalyst to and from the reactor during the course of operation. A catalyst for which particle diameter has been adjusted to a fixed range is disclosed as being used for the catalyst used in the fluidized bed reaction in order to reduce catalyst loss due to dispersion during the reaction or improve fluidity.
Patent document 2 discloses, as an example that focuses on catalyst fluidity, an example of an ammoxidation reaction that uses propylene or isobutylene for the raw material. In this document, it is disclosed that the content of particles having a particle diameter within a range of from 5 to 150 μm is 95% by mass or more, the content of particles having a particle diameter within a range of from 20 to 30 μm is from 3 to 30% by mass, a high nitrile yield is obtained due to being able to achieve a favorable fluidized state, and that catalyst loss is reduced.
Patent document 3 discloses a vapor-phase oxidation reaction by which a molybdenum compound released from a metal oxide catalyst precipitates in the form of acicular crystals on the surface of a reaction apparatus, wherein as a result of reacting using a catalyst in which the proportion of catalyst particles having a particle diameter of 20 μm or less is 2% by mass or less, the intermingling and solidification of small particles among the acicular crystals decreases, and decreases in the heat transfer coefficient of the heat dissipating coil within the reactor, obstruction of lines, increases in catalyst consumption, and coverage of the inner surface of the reaction apparatus by catalyst particles can be prevented.
In addition, Patent documents 4 and 5 (Japanese Patent Application Laid-open Nos. S52-140490 and 2001-29788) disclose processes for separating dry particles outside a desired particle diameter range by applying dry particles obtained from a spray dryer to a classification procedure, crushing the separated dry particles, and reusing by mixing into a slurry prior to spray drying.
Patent document 1: International Patent Publication WO 2004/108278 pamphlet
Patent document 2: Japanese Patent Application Laid-open No. 2002-233768
Patent document 3: Japanese Patent Application Laid-open No: 2006-248919
Patent document 4: Japanese Patent Application Laid-open No. S52-140490
Patent document 5: Japanese Patent Application Laid-open No. 2001-29788